A. Field of the Invention
The present invention relates to connectors for use with coaxial cables used to carry high frequency analog signals such as video, television, satellite signals, and high-speed digital data signals. More particularly, the invention relates to a coaxial connector of novel design which facilitates connecting and disconnecting the connector to target mating connectors of various types, with greater speed and less likelihood of mis-aligning or cross-threading the target connector than possible with pre-existing connectors.
B. Description of Background Art
There are available a variety of connector types for connecting the conductors of a coaxial electrical signal cable with corresponding conductors of another cable or with an electronic device such as a satellite or television receiver or antenna, electronic test instrument, computer apparatus or the like. A typical electrical connection, between a coaxial cable carrying high-frequency analog or digital electrical signals and another cable or an electronic device uses a mateable pair of releasably engageable, complementary connectors. Such connector pairs typically consist of a male connector part which has an outer tubular cylindrical conductive tube that is joined at a rear end thereof to a braided conductive metal sheath which serves as the outer, low potential conductor of a coaxial cable. The male connector part has located within the conductive tube, a central coaxially located axial connector pin which is in electrically conductive contact with, or is forwardly extended portion of, a central conductor of the coaxial cable. The center axial pin of the male coaxial connector part usually extends to the front transverse annular end wall of the outer tube of the connector, or slightly beyond.
A typical female coaxial connector part for mating with a male connector part of the type described above typically includes an elongated outer conductive shell which is adapted to fit coaxially within and make electrically conductive conduct with the inner cylindrical surface of the male connector tube. The rear part of the shell is conductively connected to a rear connector termination, such as the outer conductive sheath of another coaxial cable, or a ground plane of
a printed circuit board, for example. The bore of the outer shell of a female coaxial connector usually contains a cylinder made of an insulating material such as PTFE which has good high-frequency dielectric properties. The female connector also has protruding longitudinally rearwards from the flat front transverse face of the dielectric cylinder an elongated conductive ferrule which is electrically connected to a rear center conductor termination of the female connector. The ferrule typically has a chamfered front entrance opening and is elastically deformable in diameter, to thereby receive in a tight compression fit the center axial pin of the male connector, when the two connector parts are pressed longitudinally together.
Some coaxial connector pairs of the type described above are constructed in a way that permits the two parts of the connector to be electrically and mechanically connected simply by inserting the female connector outer shell into the male connector tube bore. Such “push-on,” or “quick” connectors typically use a resiliently outwardly deformable male connector tube to frictionally retain the inserted female shell within the bore of the tube. To provide this resilient deformability, typical male push-on connectors have one or more slots which extend longitudinally rearward from the front transverse face of the tube, forming therebetween a resiliently deformable tab. The tube is made of a springy metal, and has an undeformed inner diameter slightly less than the outer diameter of the female connector shell, thus enabling the tabs of the male tube to resiliently deform radially outwardly and grip the female shell when the shell is inserted into the bore of the tube.
Although push-on connectors of the type described above are sometimes used in indoor applications, such use is generally confined to low frequency video applications, because of their poor RF characteristics as compared to threaded connectors. Moreover, they are unsuitable for outdoor use because typical push-on connectors are not water-tight, and therefore may admit dust as well as atmospheric moisture in the form of rain or condensation into the interior of the connector pair. Such moisture is problematic not only because it can corrode and degrade connector components, but because it can substantially alter both DC and RF electrical properties of the connector pair. Thus, as is well known to those skilled in the art, connecting a coaxial cable of a particular characteristic impedance to a mismatched impedance caused by variations in electrical properties of a connector will result in significant signal insertion loss and reflections.
For the foregoing reasons, coaxial connections made to satellite antenna dishes, off-air television antennas and other outdoors equipment routinely are made using coaxial connector pairs in which the female shell has external threads that engage internal threads on the inner surface of the male connector tube. Such connectors suitable for use outdoors usually include a resilient rubber O-ring or flat washer seated at a rear flange wall located at the inner end of the male tube. When the threaded female shell is threadingly advanced sufficiently far into the bore of the male connector tube, the front transverse wall of the female connector part compresses the O-ring or washer to form a water-tight seal. To further ensure against water penetration into mating parts of the connector pair halves, a tubular boot made of a water-impervious, elastomeric material such as silicone rubber is sometimes fitted over mating connector parts.
A widely used threaded coaxial connector of the type described above is referred to as an “F-connector.” Male and female F-connector parts typically have threads which span the full length of the inner tube surface or outer shell surface, respectively. Each connector part can have a relatively large number of threads, e.g., 5-8 or more.
One of the problems with fully-threaded connectors is that when they are deployed in the field for a period, and exposed to weather conditions, the connectors often become dirty, corroded and difficult to unscrew without the use of a wrench. But often the connectors are grouped so closely together that there is simply no space for a wrench. Corrosion occurs because the rubber O-ring at the bottom of the male connector may stop water and moisture from reaching the inner conductors, but water and dirt can still penetrate voids between mating connector threads. Therefore, the more threads there are on a connector, the harder it may become to unscrew the connector after exposure to the elements.
Furthermore, conventional screw-on, screw-off operations become laborious when the number of connections to be made is increased. As a result, an installer may fail to screw a connector in all the way, thus again resulting in moisture entering the connector even if there is a rubber O-ring seal at the base of the male-connector.
Moisture in a connection changes the system characteristic impedance and causes RF signal reflection, a very undesirable condition in any video or RF frequency application, which can be characterized as a degradation in Return Loss (RL). Return Loss is a measure of how closely the impedance of a source matches that of a load. A mis-match causes degradation of signal power transfer and degradation of system frequency response. To combat the moisture problem, a “weather boot” is often employed. But weather boots are bulky and of limited use in tight spaces. The weather boot is somewhat water-proof but not moisture-proof. Also, changes in temperature during the days and the nights can cause moisture to be admitted into the connection.
Another problem with fully-threaded connectors is initial alignment. The connectors will not mate if they are not perfectly aligned, necessitating trial-and-error time to be expended by an installation technician. Mis-alignment can result in cross-threading, and may damage the male and/or female threads if forced, thus making removal even more difficult. Since cross-threading often results in imperfect mating, the potential of allowing water and/or moisture to accumulate in the connector cavity is increased, even if the intended rubber “O” ring is in place.
As stated above, one prior art solution for solving the difficulties of fully-threaded connectors has been to use a non-threaded, push-on male connector. But connections made by push-on connectors are not water/moisture-sealed, and allow water/moisture to seep into the connectors, thus degrading the performance and causing poor Return Loss (RL). This results in system degradation.
Also, a push-on connection can be pulled off very easily. Equally troublesome, a connection may be pulled loose but allow connectors to hang onto each other. The installer often cannot tell if a connection is loose, thus spending unnecessary time trying to trouble shoot system problems elsewhere.
A less obvious problem with push-on connectors is that even when seated properly, a push-on connection has an inferior RL performance compared to that of the equivalent threaded types and is best used for lower-frequency applications, rather than the high frequencies employed in fields such as satellite signal distribution and the cable industry's HDTV signal distribution.
The present invention was conceived of to provide an improved coaxial connector which overcomes problems associated with prior art coaxial connectors of the type described above.